Magnetic Particle Inspections are used to detect surface and slightly subsurface flaws and defects using magnetic fields and small magnetic particles.
The process puts a magnetic field into the part. The piece can be magnetized by direct or indirect magnetization.The presence of a surface or subsurface discontinuity in the material allows the magnetic flux to leak.Ferrous iron particles are then applied to the part. The particles may be dry or in a wet suspension. If an area of flux leakage is present, the particles will be attracted to this area.
Types of flaws that can be detected with MT
This method is used to detect surface and slightly subsurface discontinuities.
Types of material that can be tested using MT
This method is used on a variety of product forms including castings, forgings, and weldments. The material must be ferroelectric – such as iron, nickel, cobalt or a related alloy.
Advantages of using MT
There are many advantages to MT Testing including:
- MPI/MT can locate both surface and near sub-surface flaws and defects
- Testing is portable and cost-effective
- Immediate results
- Indications are visible directly on the components surface
- Parts with irregular shapes can be tested using this method (crankshafts, connecting rods, etc.)
Disadvantages of using MT
Although Magnetic Particle Inspections are a great tool, it is important to remember a few things:
- The component must be ferromagnetic (e.g. steel, cast iron)
- Paint thicker than ~ 0.005″ must be removed prior to the inspection
- Post cleaning and post demagnetization is often necessary
- Maximum depth sensitivity is typically quoted as 0.050 to 0.100
- Alignment between magnetic flux and defect is important
Industries that use MT
MT can be used in many industries including:
- Structural Steel
- Power Generation